© Michael Lacewing
The problem of other minds
THE THREAT OF SOLIPSISM
The problem of other minds is the question of how we can know that there are
minds other than our own. We each experience our own minds directly, from
‘within’. We can each apprehend our sensations and emotions in a way that is
‘felt’. We can know what we want or believe through introspection. But our
knowledge of other people’s minds is very different, it seems. We cannot
experience other people’s mental states. It seems that all we have to go on is
other people’s behaviour, what is expressed through their bodies.
This has been thought to raise an important challenge for substance dualism. If
minds and bodies are entirely independent, then how can I infer from seeing a
body that there is a mind ‘attached’? Other ‘people’ – other bodies – could all be
machines, programmed to behave as they do, but with no minds. If there are no
other minds, then my mind is the only one that exists. This is solipsism. The
challenge to substance dualism is, how do we know that other minds exist and
solipsism is false?
THE ARGUMENT FROM ANALOGY
The argument from analogy claims that we can use the behaviour of other people
to infer that they have minds too. It was first presented by John Stuart Mill. (The
first form is often attributed to Mill, but the second form is a better
interpretation.)
1. I have a mind.
2. I know from experience that my mental states cause my behaviour.
3. Other people have bodies similar to mine and behave similarly to me in similar
situations.
4. Therefore, by analogy, their behaviour has the same type of cause as my
behaviour, namely mental states.
5. Therefore, other people have minds.
The argument is perhaps the ‘common-sense’ position on how to solve the
problem of other minds. But we can object to its use of induction. The conclusion
that other people have minds is based on a single case – mine. This is like saying
‘that dog has three legs; therefore, all dogs have three legs’. You can’t generalize
from one case, because it could be a special case. Perhaps I am the only person to
have a mind.
However, instead of talking about the causal relation in the single case of my
behaviour and my mind, we can formulate the argument to cite many instances of
behaviour which we know to have a mental cause.
1. This behaviour has a mental cause.
2.
3.
4.
5.
That behaviour has a mental cause.
That third behaviour has a mental cause.
Etc.
Therefore, many behaviours have a mental cause (I know this from my own
experience).
6. Other people exhibit the same types of behaviour as cited above.
7. Therefore, those behaviours also have mental causes.
8. Therefore, other people have minds.
Can we object that the argument still relies on analogy, on the contentious claim
that like effects (behaviour) have like causes (mental states)? For example, even if
behaviour in my case is caused by (my) mental states, that doesn’t mean that the
behaviour of other people could not be caused by something entirely different
(say, brain states without mental states).
This objection misunderstands how the argument is intended to work. First, the
behaviour picked out in the first premises of the argument is not picked out as
mine, but as a type of behaviour, e.g. raising an arm, walking to the shops, etc.
The claim is that we have experience of many instances of such behaviour being
caused by mental states. Now, in science, we generalize from the cases we have
observed. ‘Water boils at 100 degrees Celsius’ (at sea level) – we haven’t
measured the temperature in every case of boiling water, but each time we do,
we get the same result, so we make the general claim. We can do the same with
behaviour. On this understanding, the argument is not from analogy at all. It is
simply a causal inference.
Second, of course the sceptical claim that these instances are exceptional, that
the behaviour of other people has a different cause, remains possible (just as it is
possible that water doesn’t always boil at 100 degrees Celsius). But the argument
is only intended to make belief in other minds justified. We can think of it as an
inference to the best explanation.
The solution still faces difficulties. First, it relies on mental causation, in this
case, behaviour being caused by mental states. This is something that substance
dualism has difficulties in explaining. But we can respond that we only need the
claim that behaviour is caused by mental states, not an explanation of how.
Second, we can object that the belief that other people have minds is not a
hypothesis, nor do we infer, on the basis of evidence, that they have minds. This
whole way of understanding the way we think about other minds is mistaken.
ON ASCRIBING MENTAL STATES
Descartes and solipsists assume that we can ascribe mental states to ourselves, to
say of oneself that one is thinking, or that one wants to understand, or that one is
frustrated. But what does this ability require? We can argue that, for instance, a
child cannot learn that it is angry, that what it feels is ‘anger’, without also
learning what it means to say, of someone else, that they are angry. After all, it
learns that it is angry because its parents (and others) help it understand this. One
way in which they do this is for the parents to point out when they or other people
are angry, and how this is similar to when the child is angry. So the child also
learns how to recognize when other people are angry. The ability to ascribe
mental states to oneself is learned, and is interdependent with the ability to
ascribe mental states to other people. To learn the meaning of ‘anger’, ‘pain’,
thinking’ is to learn their correct application to both oneself and others,
simultaneously. In that case, to understand a mental property, I have to be able to
attribute it to other people. I have to be able to say ‘he is in pain’ or ‘she is
thinking’.
This has a number of important implications.
1. If there can be no knowledge of oneself as a mind without presupposing that
there are other minds, the problem of other minds does not arise.
2. Our knowledge of other minds is not inferred from knowledge of our own
behaviour and its causes. We don’t have one without the other.
3. It raises a distinct challenge to substance dualism. Substance dualism claims
that mental properties are attributed to minds, while physical properties are
attributed to bodies. But in that case, how can we identify other minds so as to
attribute mental properties to them? We have no experience of ‘minds’ on their
own. So we have to attribute mental properties to something that also has
physical properties. Mental and physical properties have to be attributed to the
same thing for us to attribute mental characteristics to anything at all. This
threatens the claim that the mind is a separate substance from the body.
4. It raises a challenge to the substance dualist’s concept of mind. We don’t know
what a mind is unless we already know what a person – an ‘embodied mind’ –
is. We can only understand the idea of a mind by abstracting from the idea of a
person; a mind is a disembodied person. In other words, the concept of the
‘union’ of mind and body is a more basic concept than the concept of mind.